Sensitive pressure switch



P 1952 A. v. c. DAVIS 3,056,004

SENSITIVE. PRESSURE SWITCH Filed Afig. 10. 1959 4 Sheets- Sheet 1 biga.

@YMMQQQM Sept. 25, 1962 A. v. c. DAVIS 3,056,004

SENSITIVE PRESSURE SWITCH Filed Aug. 10, 1959 4 Sheets-Sheet 2 6 3 I I IINVENTOR. @2267: 6106x228.

P 25, 1962 A. v. c. DAVIS 3,056,004

SENSITIVE PRESSURE SWITCH Filed Aug. 10, 1959 4 Sheets-Sheet 3 INV ENTOR. @zzkk Caavzls'.

United States Patent Ofifice 3,056,004 Patented Sept. 25, 1962 3,056,004SENSITIVE PRESSURE SWITCH Allen V. C. Davis, 5600 Alta Canyada Road, LaCanada, Calif. Filed Aug. 10, 1959, Ser. No. 832,749 39 Claims. (Cl.200-83) This invention relates to pressure switches and moreparticularly to an improved form thereof characterized by extremelysmall differentials between the greater of two fluid pressures whichcauses the switches to operate in one direction and the lesser pressurewhich allows the switch to operate by spring action in the oppositdirection.

Commonly, the response of a pressure switch to the greater pressure istermed the actuation of the switch and the response to the lowerpressure is termed the reactuation. Also, commonly, the range or gapbetween the actuating and re-actuating pressures is known as the deadhand. These terms, having been defined, will be employed in thedescription of the invention to bring into such description theterminology generally employed in the art to which the inventionpertains.

In my prior Patent Number 2,824,919, dated February 25, 1958, there isshown a pressure switch in which the pressure acts on a diaphragm whichthrough a rigid pressure plate and a negative rate spring means such as,for example, a Belleville type spring capable of snap action, yieldinglyresists applied pressure. The imposition of pressure of a predeterminedmagnitude on the diaphragm and pressure plate causes the Bellevillespring to partake of snap action, the Belleville spring having such aheight to thickness (ht) ratio as to partake of snap action, and thesnap action, in turn, operates a snap action electric switch.Thereafter, upon a decrease in pressure to a given extent, the powerstored in this Belleville spring is released and the diaphragm isreturned to its. initial position by the return snap action(re-actuation) movement of the Belleville spring and of the switch.

The present invention is directed to and contemplates improved means formaking pressure switches having even narrower dead bands than theswitches of the said patent. Broadly stated, the principle involved isthat of at least partially replacing the energy loss through hysterisisincident to actuation of the switch so that a lesser difierential ordead band exists between the actuating and reactuating pressures.

Accordingly, it is an object of the present invention to provide apressure switch having means, including negative rate spring means,effective to impose a bias on a pressure responsive means which respondsto predetermined changes in applied fluid pressure with snap action, thebias being of such magnitude that when modifyingly applied to thepressure imposed load, a very slight change in the fluid pressure willeffect the defiection of the pressure responsive means with at least aportion of the said modifyingly applied load then being rendered idleuntil the switch is returned through reactuation pressure to its formerposition.

Another object of the inVentiOn i to provide a pressure actuated switchembodying the above-stated principle of the application of a bia on apressure responsive element of the switch in the direction of movementincident to actuation thereof and in which the said bias is provided byelectro-magnetic means.

A further object of the invention is to provide a pressure actuatedswitch embodying the above-stated principle of the application of a biasthereon in the direction of movement incident to actuation thereof inwhich the said bias is provided by a pressure actuated means other thanthat to which the switch responds for its pressure responsive action.

Still another object of the invention is to provide a pressure switchincluding a solenoid having the moving element thereof (usually tharmature) arranged to supply a modifying bias on the pressure responsivemeans of a snap action pressure switch which i in addition to the loadapplied thereon by an actuating fluid pressure.

A still further object of the invention is to provide means in a snapaction pressure switch which includes a pressure responsive element andmechanism actuated thereby for operation of a snap switch and embodyingmeans for applying a modifying bias thereon to reduce the width of thedead band between the actuating and re-actuating pressures and in whichthe bias applying means comprises a piston and a cylinder together withan electro-magnetic valv means for admitting pressure to the piston inan amount suflicient to apply the desired bias to the pressureresponsive switch actuating element of th pressure switch mechanism.

A still further object of the invention i the provision in a snap actionpressure switch having a pressure responsive diaphragm of means forproviding an added loading to the diaphragm and in the same direction asthe pressure load applied thereon, said loading being applied onlyduring the actuating cycle or movement of the switch.

A still further object of the invention is to provide a pressureresponsive switch with a solenoid and armature operative during onecycle of switch operation (actuation or re-actuation) to apply an addedload to the pressure responsive element of the switch.

With the foregoing objects in view, together with such other objects andadvantages as may subsequently appear, the invention resides in theparts, and in the construction, combination and arrangement of partsdescribed, by way of example, in the following specification of certainpresently preferred embodiments of the invention, reference being had tothe accompanying drawings which form a part of said specification and inwhich drawings FIGS. 1 through 11 illustrate the application of theprinciples of the invention to various forms of pressure switchesthrough the use of a solenoid and in which:

FIGS. 1 through 11 illustrate a first embodiment of the invention inwhich:

FIG. 1 is a side elevation of a pressure switch embodying the presentinvention,

FIG. 2 is a top plan view of the pressure switch shown in FIG. 1,

FIG. 3 is a greatly enlarged sectional view taken on the staggered line33 of FIG. 1,

FIG. 4 is a circuit diagram of the electrical portion of the pressureswitch,

FIG. 5 is a side elevational view of a second form of the firstembodiment of the invention,

FIG. 6 is an enlarged view in partial medial section) taken on thestaggered line 6-6 of FIG. 5,

FIG. 7 is a reduced scale, transverse sectional view taken on the line77 of FIG. 6,

FIG. 8 is a greatly enlarged, fragmentary sectional view of the aneroidelement shown in FIGS. 6 and 7,

FIG. 9 is a side elevational view of a third form of the firstembodiment of the invention,

FIG. 10 is a greatly enlarged view in partial medial section of thepressure switch shown in FIG. 9, the view being taken on the staggeredline 10-10 of said FIG. 9,

FIG. 11 is a slightly reduced scale, medial, sectional view of apressure switch generally similar to that shown in FIG. 3 except for theemployment of a solenoid which, upon energization, affects the bias onthe pressure responsive switch actuator through a tension spring,

FIGS. 12 through 15 constitute a second embodiment of the invention andillustrate the application of the principles of the invention by the useof fluid pressure as a biasing means for the pressure responsive switchactuator and in which:

FIG. 12 is a top plan view of one form of the said second embodiment ofthe invention,

FIG. 13 is a sectional view taken on the line 13--13 of FIG. 12,

FIG. 14 is a top plan View of a second form of the said secondembodiment of the invention, and

FIG. 15 is a sectional view taken on the line 15-15 of FIG. 14.

Referring first to FIGS. 1 through 4, the device there shown comprises abase 1 of generally circular outline having an axially extending sleeveportion 2; said axial portion having a laterally extending boss 3containing a threaded port 4 for connection to a source of pressure. Thesleeve portion 2 is hollow and is internally threaded from the outer endthereof to a point adjacent the inner face of the body member as at 5and terminates at the inner face of the body member in a smooth boreportion 6.

The inner end of the bore 6 is surrounded by an annular wall portion 7serving as an abutment and stop member for a diaphragm 8 the peripheraledge of which is clamped between the adjacent faces of the base 1 andthe cap member 9 by a series of screws 10. Preferably, for alignmentpurposes, the base 1 is provided with an annular bead 11 engaging acorresponding annular recess 12 in the mating face of the cap member 9.A passage 13 connects the inlet port 4 with the axial bore extendingthrough the member 2 and passages 14, 14 connect said bore with thespace 15 extending between the outer periphery of the annular wall 7 andthe juncture of the member 1 with the diaphragm at the outer edgethereof. Accordingly, fluid pressure entering through the inlet portwill pass through the passage 13 and into the bores 5 and 6 and thencethrough the passages 14, 14 will impinge upon the diaphragm 8 to urge itin a direction away from the adjacent inner face of the base member 1.

To effect snap type actuation and re-actuation of the diaphragm, the capmember 9 has an annular ledge 16 disposed adjacent to the diaphragmengaging face and on which rests the outer dameter of a Bellevillespring 17, the spring having an hzt ratio of not less than about 1.411so that a portion of its movement has a negative rate. The openingconstituting the inner diameter of the Belleville spring is filled by aplug element 18 having a shoulder 19 engaging the face of the Bellevillespring opposite the face engaging the ledge 16. The diaphragm 8 liesdirectly upon the Belleville spring and upon the exposed face of theplug element 18. At its center, the plug element is provided with anaxially extending boss 20 having an annular groove 21 extending aroundit. The groove is engaged by the free end of an arm 22 of a rock memberassembly including a connecting rivet element 23, a second arm 24extending generally parallel to but spaced from the arm 23 and aresilient, corrugated, thin metal disk 25 surrounding and secured to therivet element 23 at about the midlength thereof and having its outerperipheral edge disposed and secured by soldering or brazing in acircular recess 26 comprising an opening in the wall of the cap element9; the resilient disk 25 serving in effect, as a hinge element wherebymovements of the diaphragm and consequently of the Belleville Spring andplug element are transmitted through the rock frame to the plunger 27 ofan electric switch 28 mounted on a bracket 29 carried by the cap member9. A cover 31 secured to the outer face of the cap member 9 serves toenclose the switch and said cover may terminate either in a grommet orin appropriate socket type electrical connecting means such as at 32'which is connected within the cover to the switch terminals as, forexample, the terminals 33a, 33b and 33c of the switch 28.

Threadedly engaging the outer end of the threaded portion 5 of thesleeve member 2 is the base member 34 of a solenoid assembly generallyindicated at 35; said solenoid having a socket means 35 for electricalconnection to a source of energy. The base member 34 includes alaterally extending flange 36 supporting a cylindrical cover 37 securedthereto by screws 37' and also includes an axially extending Pole piece38 disposed within the solenoid winding 39 for about half the length ofthe winding. The winding is mounted on a sleeve 40 having one endresting on the flange 36 the opposite end being closed by a plug element41. Freely slidably mounted within the tube 40 is the armature 42 formedof paramagnetic material and which is internally threaded and threadedlysecured to the end of a rod 43 and locked thereon by a setscrew 44. Therod 43 extends through an axial bore 45 in the boss 38 and is guided bya reduced diameter concentric bore 46 at the outer face of the flange36. A compression spring 47 extending between the shoulder formed by thebores 45 and 46 and the end of the armature 42 tends to urge thearmature outwardly in the sleeve 40 and away from the adjacent end ofthe boss 38.

The outer face of the Pole piece 38 is provided with a circumferentialgroove 48 in which an O-ring 49 is seated and which engages the innerface of the tube or sleeve 40.

The bore 6 in the base member 1 slidably accommodates a plug element 50the face of which rests upon the diaphragm 8. The opposite face of theplug element 50 contains a cylindrical recess 51 interrupted at itscenter by a cylindrical boss 52. A compression spring 53 has one endthereof surrounding and positioned by the boss 52 and said spring thenceextends axially of the 'bore 5 and the opposite end thereof engages ashoulder 54 on a nut 55 carried by the threaded end 56 of the rod 43.Threadedly mounted in the threaded bore 5 of the sleeve 2 is an abutmentelement 57 having an axial bore extending therethrough through which thespring 53 extends. The outer periphery of the recess 51 in the plug 50engages and positions one end of a second compression spring 58 theopposite end of which engages a cylindrical recess 59 in the adjacentface of the plug element 57. Thus both of these springs, 53 and 58,apply loads to the plug element 50 and hence to the diaphragm andBelleville spring while the opposite ends of these springs areseparately adjustable, the spring 53 being adjusted for the imposed loadby re-positioning of the nut 55 on the rod 43 and the load exerted bythe spring 58 being determined by the position of the abutment element57 in the threaded bore 5.

It is to be noted that the pressure fluid media entering the port 4reaches the interior of the bore 6 through the passage 13 and thencethrough the passages 14, 14 and exerts its pressure against thediaphragm 8. The pressure also will extend through the adjusting nut 57and thence through the bore 46 enter the sleeve 40 of the solenoid,escape from the solenoid being prevented by the gasket 49. Thus, thepressure entirely surrounds the armature 42 and the static pressurethereon is balanced, and thus having no effect upon the movement of thearmature. However, the rate of movement of the armature is retarded bythe presence of the fluid and this damps the armature sufiiciently toprevent overtravel when the solenoid is energized.

Referring now to FIG. 4 there is shown diagramtioally a generalarrangement of the pressure switch and its biasing means, the diagramillustrating the device in the position shown in FIG. 3. In this view,the solenoid 35 is energized applying its bias through the spring 53 tothe diaphragm in addition to that of the spring 58 and the Bellevillespring and in addition to the pressure load thereon. The switch 28 isclosed in the direction connecting the solenoid to the source of energyrepresented at B. When the accumulated pressure efiects snap action ofthe Belleville spring, the switch 28 is actuated to connect anothercontact and disconnect the current to the solenoid. The changed positionof the switch actuates whatever pressure control means is connected tobe actu ated at that time, to, for example, stop the pump means whichhas been responsible for the increase in pressure or whatever otherdevices may be employed to achieve that result. This continues until thepressure has decreased sufficiently to permit the Belleville spring 17to return to its normal position by snap action or, in other words, tore-actuate. Thus it is that when the switch has reactuated and returnedto its normal position it is then subjected to a predetermined extent ofbias in the direction in which it is intended to actuate so that anextremely small increase in pressure is all that is required to cause itto actuate. Accordingly, the dead band is thus reduced to a great extentbelow that which could be otherwise achieved. It will be seen that thusrelieving the additional pre-load applied by the solenoid when actuationhas taken place enables the re-actuation to occur at a pressure decreasewhich is extremely close to the pressure which caused the initialactuation of the switch. Alternatively, the solenoid coil might, in someinstallations of the pressure switch, be connected to the switch contact330, as will be hereinafter shown, and it is equally possible that insome installations the pressure controlling means might be connected towhichever one of the contacts, 33b or 330, was connected to thesolenoid, dependent upon the requirements of the system in which thepressure switch is employed. For this reason the diagram shown in FIG. 4is to be regarded as representative of one type of installation only. itwill also be appreciated that any plunger operated switch, whethersingle or double throw, or single or multiple pole, may be substitutedfor the switch illustrated so long as it is capable of actuation andre-actuation by the pressure responsive means and that this applies toall embodiments of the invention.

Referring next to the invention shown in FIGS. 5 through 8, allcorresponding parts which have been previously described have been giventhe same numbers as applied in the preceding figures and, if referred toat all, will be referred to only incidentally. In these figures, theswitch actuator comprises an aneroid capsule indicated at 8. This formof the invention is intended for use as a vacuum responsive switch or asan altitude responsive switch, it being arranged to respond by snapaction to some predetermined pressure less than, say, sea levelatmospheric pressure.

The aneroid cell 8 is a hollow disk-like cell formed of slightly cuppedthin metal disks 61 and 621 which are secured together by soldering orwelding around their edges. As an incident to the manufacture of thecell, the air is evacuated therefrom to a desired extent which, usually,is as nearly completely as possible and may either be a complete vacuumor a partial vacuum dependent upon the degree of temperaturecompensation required. The members 61 and 62 are normally urged awayfrom each other by a Belleville spring 63 disposed within the cell andhaving its outer edge seated on a ring 64- adjacent the rim of themember 61, said ring having an edge forming a shoulder to center theBelleville spring thereon and to keep the edge of the Belleville springfrom contacting the thin, very flexible metal comprising the cell walls.The inner diameter of the Belleville spring 63 engages a shoulder 65formed in the periphery of a plug element 66 extending through theopening in the Belleville spring and resting upon and forming a supportfor the central portion of the cell wall 61.

In this form of the invention, the base 1 and cap member 9 are securedtogether by screws 10 in the usual manner but a gasket It) issubstituted for the diaphragm shown in the first form of the invention.The opposed end faces of the base 1 and cap 9 thus form an enclosedchamber 67 which is connected to the source of pressure to which thecell responds through the passages 14, 14, the bore 6, the passage 13,and the port 4. The cap member 9 includes an annular ledge 68 disposedinwardly of the end face thereof upon which the wall member 62 of theaneroid is mounted. The inner periphery of the cap member 9 adjacent theend face thereof is provided with an annular groove 69 in which a snapring 70 is seated resting upon the rim 71 formed by the closing seam ofthe aneroid cell to hold the cell firmly seated on the ledge 68. Fixedto the outer surface of the central portion of the cell wall member 61is a stud element 72' having an annular groove 21' formed therein inwhich the arm 22, of the rock frame 23 is engaged. The rock frameincludes, as in the first form of the invention, an arm 24 connected tothe arm 22' by a rivet element 23 and a resilient disk element 25secures the rock frame in a circular recess 26 in the cap element 9, therock frame arm 24 actuating the plunger 27 of a switch 28 carried by abracket 29' mounted on the outer surface of the cap member 9. Outwardly,beyond the annular groove 21', the stud member 72 includes a largerdiameter portion which engages the end face of the plug element 50. Itis to be noted that the rock frame arm 2-2 extends radially away fromthe groove 21 thence extends around the edge of the aneroid cell andthence radially back toward the axial line of the pressure cell for ashort distance at which point it is connected to the rivet element 23.The ledge 68 is interrupted to provide a gap through which bent portionof the arm 22 may extend past the edge of the aneroid cell to theopposite side thereof. Likewise, the end of the snap ring are separatedsufiiciently to complement this gap. Additionally, the end wall 7surrounding the end of the bore 6 adjacent the cell containing cavity 67is provided with a radially extending gap to afford clearance for thefree end of the arm 22 as it is moved by the action of the cell 8. Theend of this annular Wall also serves as a stop element to limit theoutward movement of the cell wall 61.

Assuming that the device is to be used as a switch which is responsiveto some given altitude condition, the port 4 is connected to or leftopen to atmosphere. At sea level and up to some predetermined altitudethe air pressure then within the cavity 67 would maintain the aneroidcell collapsed. When the pressure in the cavity 67 was reduced to somepredetermined extent by reason of increased altitude, the Bellevillesprim would snap to the position shown in FIG. 8 with consequentmovement of the rock frame and actuation of the switch. Such movementwould correspond to the re-actuation portion of the cycle of the firstdescribed invention and as an incident thereto the solenoid would beenergized to apply a bias to the pressure cell in opposition to theBelleville spring within the cell or capsule 8 until such time asthrough descent or other conditions the pressure in the cavity 67increased to a point at which the opposition thereto by the Bellevillespring is overcome and the Belleville spning moved by snap actionallowing the aneroid cell to collapse with consequent actuating movementof the rock frame and of the switch 28. A switch of this character wouldbe useful, for example, in cabin pressure maintaining systems or in anyother aircraft system in which the indication of a given altitude or ofa given atmospheric pressure less than sea level was essential. It isbelieved to be obvious that even though the Belleville springs used inthe aneroid cells may vary some in individual characteristics, suitableadjustment of the load imposed by the solenoid through the springs 53and 58 can compensate for such differences so that through appropriateadjustments a series of switches having Belleville springs of differentcharacteristics enclosed within the capsule can be brought intoadjustment for actuation and re-actuation in a uniform manner for agiven set of pressure conditions. The bias imposed in one direction bythe solenoid acts to replace the work lost to the operation of theswitch and the hysterisis of the parts and thus narrows the dead band ofthe switch so that it will actuate and re-actuate at very closedifferences in. pressures.

Referring next to the form of the first embodiment of the inventionshown in FIGS. 9 and 10, again, all parts disclosed which are similar toparts described in detail in preceding figures have been given the samenumbers and will be referred to only incidentally in the description ofthis form.

The pressure responsive actuator here comprises the diaphragm 8 havingits periphery clamped between the adjacent faces of the base member 1and cap member 9 in the same manner as in FIGS. 1 through 4. Thediaphragm, however, lies closely against the end face of the base member1 and this base member is provided with a series of radially extendinggrooves 73 leading from the discharge ends of the passages 14, 14 andintersecting a series of annular grooves 74 disposed concentrically witheach other about the axial line of the bore 6. The grooves 73 and 74serve to distribute the pressure evenly over the surface of thediaphragm. The diaphragm is normally held pressed against the end faceof the base member 1 by a rigid pressure plate 7 which is ofsubstantially the same diameter as the free area of the diaphragm 8".The pressure plate carries an annular shoulder 7 6 which engages theinner diameter of a Belleville spring '77, the outer periphery of whichis mounted in a shoulder 78 formed in a circular rim or wall 79 on theinner face of the cap member 9. The pressure plate 75- on the sideopposite the diaphragm additionally carries an axially projecting studelement 80 having the annular groove 21 formed therein for reception ofthe arm 22 of the rock frame which includes the connecting rivet 23, thearm 24, the resilient disk 25 anchored in the recess 26 in the capmember 9, the free end of the arm 24 serving to operate the plunger 27of a switch 28 carried by the bracket 29. Additionally, the cap member 9carries a port 81 which communicates with the interior of the cap member9 at the side of the diaphragm opposite that which is in communicationwith the port 4, the diaphragm forming a flexible partition interposedbetween the ports 4 and 81. When the port 81 is also connected to asource of pressure, the pressure switch acts in response to pressurediiierentials between the sources of pressure to which the ports 81 and4 are, respectively, connected. In this connection, it will beappreciated that other illustrated forms of the invention can similarilybe provided with a second port on the opposite side of the diaphragm forservice as differential pressure switches.

The operation of this form of switch is believed to be obvious from thedescription of the two precedin embodiments of the invention. Normally,the switch is in the position shown in section in FIG. in whlc'hposition the solenoid is energized and is applying its load to thediaphragm in addition to the pressure entering through the port 4 whichis opposed by the Belleville spring 77 and the pressure entering throughthe port 81. When the pressure entering through the port 4 in additionto the bias imposed by the solenoid and the spring 58 overcomes theresistance of the Belleville spring and the said opposing pressure, thespring moves with snap action until the surface of the pressure plate 75engages the outer end of the annular wall 79, the wall thus, in additionto serving as an anchor for the outer periphery of the Bellevillespring, acting also as a stop member to limit the movement of thepressure plate. Actuation of the switch 28 will connect one circuit anddisconnect another including the de-energization of the solenoid aspreviously described in connection with the first form of the invention.When the pressure on the side of the diaphragm supplied through the port4 decreases to a predetermined extent the Belleville spring will partakeof its re-actuation movement, returning to the position shown in FIG.10, and, of course, re-energizing the solenoid. For those uses in whicha differential between two pressure sources is unnecessary, the port 81may be left disconnected and thus open to atmosphere whereupon said portwill act merely as the necessary breather to permit the free actuationof the diaphragm and the pres sure plate in response to the pressureconditions afiecting it through the port 4.

It will be understood that when the solenoid is disabled, the spring 47will move the armature and the rod 43 away from the diaphragm releasingthe load imposed thereon by the spring 53, thus reducing the loadreduction deriving from pressure reduction to which the diaphragm willrespond by snap action. The same consideration is, of course, true withrespect to the aneroid cell or capsule which is the pressure responsiveactuating means in the second form of the first embodiment of theinvention, the disabling of the armature and release of the spring 47and 53 serving likewise to reduce the amount of pressure on the exteriorof the aneroid cell enabling it to respond to a lesser increase inapplied fluid pressure. It will be understood that the adjustment of thespring 58 corresponds generally to the adjustment to compensate fordifferences in switch response and inherent ditierences in seeminglyidentical Belleville springs as discussed in detail in my said priorpatent. The present invention is, therefore, directed particularly tothe means of imposing an additional load on the Belleville springelement of the switch which acts in addition to the actuating pressureand thus, being adjustable, permits the actuating pressure to beadjusted within a very close limit with respect to the re-actuatingpressure.

FIG. 11 illustrates the point that the solenoid previously describedneed not be one which applies a push upon the switch actuator but mayalso apply its bias 'additively, where desired, by exerting a pull uponthe primary bias producing means through a tension spring. In thisfigure, all parts which are the same as shown in FIG. 3 and whichoperate in the same manner have been given the same numbers as appliedin FIG. 3. T sleeve 2 of the base 1 is additionally externally threadedas at 82 and is engaged by the depending internally threaded sleeveportion 83 of the solenoid base 34. Th end of the sleeve portion 2 isprovided with an annular groove 85 in which an 0-ring gasket 86 isseated to prevent leakage of iluid between the solenoid base 34 and thesleeve 2. The solenoid base 34 includes an integral sleeve portion 87which extends through the solenoid and the pole piece 88 at the outerend of this sleeve is pr vided with a groove 89 containing an O-ringgasket 90 to prevent fluid leakage out of the outer end of the solenoid.The solenoid armature 91 is loosely mounted within the end of the sleeve87 adjacent to the base 34 and carries an axially disposed screwthreaded pin 92 secured in adjusted position therein by a set screw 93.The screw 92 extends into the bore 5 beyond the end of the armature 91and carries a screw threaded portion 94 engaged by one end of a tensionspring 95 which extends axially along the bore 5 and engages a plugmember 96 in the lower end of the bore 6 the outer end of which engagesthe diaphragm 8 and the said plug member being urged against thediaphragm in opposition to t e spring 95 by the compression spring 58reacting between the plug member 96 and the abutment sleeve member 57.

Normally, the full force of the spring 58 is exerted through the plugmember 96 against the diaphragm 8 and the Belleville spring 17. This,however, is opposed by the tension exerted thereon through the energizedsolenoid with the resultant pull exerted by the armature through thetension spring 95 on the plug member in opposition to the spring 58..Thus the energization of the solenoid can reduce the effect of thespring 58 to a point at which the diaphragm can respond to appliedpressure at a very slight change from that which caused the diaphragmand Belleville spring to operate in the opposite direction.

Finally, considering FIGS. l2, l3, l4 and 15, it is shown that insteadof a solenoid for applying the added bias to the pressure responsiveactuator of the switch, fluid pressure may be employed. As in previousfigures, similar 9 parts have been given the same numbers as inpreviously described figures.

In the form shown in FIGS. 12 and 13, the threaded portion of the sleeve2 is engaged at its outer end by the externally threaded neck 100 of acylinder 101 with an interposed gasket 101a, the outer end of which isinternally threaded and is closed by a cap 102 and sealed by a gasket103 interposed between the cap member and the cylinder wall. The capmember in turn is provided with an internally threaded port 104connected by a line 105 to the port 106 of a solenoid operated three-wayvalve 107 of a type available on the open market, said valve also havingan inlet port 103 and a discharge port 109.

Slidingly mounted in the cylinder 101 is a piston rod 111 extendingtherefrom through the threaded neck 100 and a sealing gasket 111acarried thereby. A gasket 112 seated in a peripheral groove in thepiston engages the side wall of the cylinder to effect a seal therewith.A compression spring 113 surrounding the piston rod 111 extends betweenthe inner face of the cylinder 114 and the adjacent face of the piston110 and operates to oppose the cifect of pressure on the piston enteringthrough the port 104, a series of lugs 115 on the fiace of the pistonengaged by the spring 113 serving to position the spring co-axially withrespect to the piston rod 111. The distal end of the piston rod 111 isspaced from the plug 50 and terminates in a reduced, diametric threadedend 1117 engaged by one end of a compression spring 118, the other endof the spring engaging the plug 50.

In addition to the pressure imposed load on the plug 50 through thepiston rod 111, further load is supplied through the spring 58 extendingbetween the plug 50 and an adjustable abutment member 116 threadedlyengaging the threaded portion 5 or" the base member 1, said memberhaving an axial bore therein through which the piston rod 111reciprocates and said bore being provided with a peripheral groove inwhich a gasket 117 is seated to prevent leakage therethrough. A seriesof holes in the outer face of the abutment member 116 as indicated at119 provides means for engagement with the abutment member by a spannerwrench for insertion, removal and adjustment of the abutment member.

When the solenoid valve 107 is energized fluid pressure will reach theinterior of the cylinder 101 through the line 105 and the pressure loadthus imposed on the piston, less the opposition thereto by the springs58, 113 and 117, will be added to that imposed by the springs 58 and theactuating pressure imposed on the diaphragm 8 through the port 4. Whenthis combined load through increase of the actuating pressure reachessome predetermined point, the load thus imposed will cause theBelleville spring to deflect with a snap action and resultant actuaionof the switch 28. The circuit diagram for the electric circuit would besimilar to that shown in FIG. 4 and upon such actuation of theBelleville spring and switch, the solenoid valve 107 would bede-energized, whereupon, the fluid would be returned through the line105 by the action of the spring 113 on the piston 110, the fluid thenceleaving the valve through the outlet port 109 thereof, it beingunderstood that when the valve is energized the port 106 is connectedwith the inlet port 108 and that when it is de-energized the port 106 isconnected with the discharge port 109. When the pressure through theport 104 has decreased to a predetermined degree, the Belleville springand diaphragm will react by the snap action of the Belleville spring andreturn to the position shown in FIG. 13. Such reiactuation will, ofcourse, reenergize the solenoid valve 107 with the resultant impositionof the bias on the pressure responsive actuator by the piston 110. Itwill thus be apparent that the operation is exactly the same as thoughthe cylinder 101 and its asso* ciated piston and springs were asolenoid.

Referring finally to FIGS. 14 and 15, the sleeve 2 of the base 1terminates at its outer end in a lateral flange 120 having an annulargroove in 121 in the outer 10 face thereof containing a gasket 122. Theouter end of the internally threaded portion 5 of the sleeve 2 isengaged by the externally threaded end 123 of a cylinder 124. The outerend of the cylinder 124 is internally threaded and is closed by a screwcap 125 having a breather hole 126 therein. Reciprocably mounted in thecylinder 124 is a piston 125 having a peripheral groove containing agasket element 127 engaging the cylinder wall. The piston 126 is carriedby a piston rod 128 extending through the end wall of the cylinder whereit is engaged by spaced O-ring gaskets 129 and 130, there being an openspace between the bearing portions containing these gaskets with which abreather hole 131 communicates. Below the threaded end of the cylinder124 the piston rod 128 terminates in a reduced diameter threaded portion132 to which one end of a tension spring 133 is connected. The other endof the tension spring 133 is connected to an eyelet 134 formed as anintegral part of a plug element 135 slidably mounted in the bore 6 ofthe base member 1. Also threadedly mounted in the threaded portion 5 ofthe sleeve member 2 is an abutment member 136 having an axial opening137 therein through which the spring 133 extends, said abutment memberalso having a shoulder 138 serving as an abutment for one end or" acompression spring 139 which surrounds and extends co-axially with thespring 133 and which, at its outer end, engages the plug member 135. Acompression spring 140 extends between the cap member 125 and the outerend of the piston tending to move the piston toward the plug member'135.A port 141 opens into the space between the piston and the end of thecylinder through which the piston rod extends, said port being adaptedto be connected to a three-way valve such as the valve 107 shown in FIG.13 and in the same manner as illustrated in that figure.

It will be appreciated that the structure here disclosed illustrates thepoint that the fluid pressure form of biasing means for a pressureswitch can operate additively through a tension spring as well asthrough a compression spring in the same manner that the solenoid mayoperate through a tension spring as illustrated in FIG. 11. Generally, apressure switch thus made would normally be in the position shown inFIG. 1.5, that is, with the Belleville spring in the position shown inthat figure and with the plug element 135 projecting out of the bore 6.The solenoid valve would be energized and pressure fluid would be in thecylinder tending to urge the piston 126 against the loads thereonimposed by the spring 140 and the spring 133, the latter being opposedby the initial loading of the spring 139. When the pressure on th switchactuating means entering through the port 4 decreased to a predeterminedextent the Belleville spring would actuate and in turn effect actuationof the switch 28 and which as in the previously described embodiments ofthe invention, in addition to whatever other functions were produced bycurrent control by the switch, would de-energize the solenoid valveallowing the spring 140 to move the piston toward the opposite end ofthe cylinder with incidental discharge of pressure fluid out of the port141 and through the discharge port of the solenoid valve.

While in the foregoing specification there have been described andillustrated certain presently preferred embodiments of the invention, itis not to be inferred therefrom that the invention is intended to belimited to such embodiments, and it will be understood that theinvention includes as well, all such changes and modifications in theparts and in the construction, combination and arrangement of parts asshall come within the purview of the appended claims.

I claim:

1. 'In a pressure switch, a frame structure including a fluid pressurereceiving chamber and means for connecting said chamber with a source offluid pressure, a switch mechanism carried by said frame structure andincluding snap action contact making and breaking devices, a

member forming a wall of said chamber movably responsive to fluidpressure variations therein, means translating pressure responsivemovements of said member into snap action movements of said switchmechanism, spring means having at least a decreasing rate constantlyoperative to apply a bias on said member to yieldingly oppose fluidpressure in said chamber; said spring means and said member beingsubject to hysteresis losses incident to the pressure responsivemovements thereof, and means for increasing the sensitivity of saidswitch to pressure changes including devices acting on said member andoperative by a power source externally of said pressure switch toyieldingly and at least partially oifset those hysteresis losses of saidspring means and said member which occur incident to movements thereofresponsive to increasing pressure in said chamber.

2. A pressure switch as claimed in claim 1 in which said devices includea solenoid having a coil connected to a source of electrical energy, anarmature and a train of mechanism extending therefrom to said member,and means for connecting said coil to the source of energy only duringthe times said member and spring means are to be subjected to switchactuating movement in response to a pressure increase.

3. A pressure switch as claimed in claim 1 in which said devices includea cylinder connected to a source of fluid pressure, a piston in saidcylinder positioned to be subjected to pressure therein, spring meansoperative to cause said piston to yieldingly oppose pressure in saidcylinder, a train of mechanism extending between said piston and saidmember and valve means operative to admit pressure to said cylinder onlyduring the times said member and said spring means are to be subjectedto switch actuating movement in response to a pressure increase.

4. In a pressure switch, a frame structure including a fluid pressurereceiving chamber and means for connecting said chamber with a source offluid pressure, a switch mechanism carried by said frame structure andincluding snap action contact making and breaking devices, a memberforming a wall of said chamber movably responsive to fluid pressurevariations therein, means translating pressure responsive movements ofsaid member into snap action movements of said switch mechanism, springmeans having at least a decreasing rate constantly operative to apply abias on said member to yieldingly oppose fluid pressure in said chamber;said spring means and said member being subject to hysteresis lossesincident to the pressure responsive movements thereof, and means forincreasing the sensitivity of said switch to pressure changes includingdevices acting on said member and operative by a power source externallyof said pressure switch to at least partially offset those hysteresislosses of said spring means and said member which occur incident tomovements thereof responsive to decreasing pressure in said chamber.

5. A pressure switch as claimed in claim 4 in which said devices includea solenoid having a coil connected to a source of electrical energy, anarmature and a train of mechanism extending therefrom to said member,and means for connecting said coil to the source of energy only duringthe times said member and spring means are to be subjected to switchactuating movement in response to a pressure decrease.

6. A pressure switch as claimed in claim 4 in which said devices includea cylinder connected to source of fluid pressure, a piston in saidcylinder positioned to be subjected to pressure therein, spring meansoperative to cause said piston to yieldingly oppose pressure in saidcylinder, a train of mechanism extending between said piston and saidmember and valve means operative to admit pressure to said cylinder onlyduring the times said member and said spring means are to be subjectedto switch actuating movement in response to a pressure decrease.

7. In a pressure switch, a switch mechanism movable with inherent snapaction in either direction between two positions and switch actuatingmeans operably associated with said switch mechanism and correspondinglymovable between two positions; said actuating means including, a membermovably responsive to fluid pressure imposed on the surface thereof,means aflording the connection of said pressure switch to a source offluid pressure with resultant imposition of fluid pressure on saidsurface of said member, and means engaging said member and yieldinglyopposing the force of fluid pressure on said member and deviceseffective to increase the sensitivity of said yielding means to pressurechanges yieldingly engaging said yielding means and operative by saidengagement to reduce the pressure opposing bias on said member when saidswitch actuating means is in a predetermined one of said two positionsto a greater extent than when said switch actuating means is in itsother position.

8. In a pressure switch, a switch mechanism movable with inherent snapaction in either direction between two positions and switch actuatingmeans operably associated with said switch mechanism and correspondinglymovable between two positions; said actuating means including, a membermovably responsive to fluid pressure imposed on the surface thereof,means affording the connection of said pressure switch to a source offluid pressure with resultant imposition of fluid pressure on saidsurface of said member, and means engaging said member and yieldinglyopposing the force of fluid pressure on said member and includingdevices controlled by said switch mechanism effective to increase thesensitivity of said yielding means to pressure changes yieldinglyengaging said yielding means and operative by said engagement to reducethe pressure opposing bias on said member when said switch actuatingmeans is in a predetermined one of said two positions to a greaterextent than when said switch actuating means is in its other position.

9. A pressure switch as claimed in claim 8 in which said devices includea solenoid controlled by said switch mechanism and having devicesinterposed between the armature thereof and said member effective toyieldingly additively oppose the bias on said member exerted by saidfirst-named fluid pressure force opposing means.

10. A pressure switch as claimed in claim 8 in which said devicesinclude a pressure responsive cylinder and piston means and yieldinglydevices interposed between said piston and said member, and controllingmeans for said cylinder and piston including a valve controlled by saidswitch mechanism.

11. In a pressure switch, a switch mechanism movable with inherent snapaction in either direction between two positions, switch actuating meansseparately movable by snap action operably associated with said switchmechanism and correspondingly movable between two positions; saidactuating means including a member movably responsive to the force offluid pressure imposed thereon, means for subjecting said member tofluid pressure, pressure opposing means engaging said member andimposing a yielding bias thereon including a spring having a negativerate, and means for increasing the sensitivity of said switch actuatingmeans to pressure changes including auxiliary devices yieldablymodifying the bias imposed on said member by said pressure opposingmeans when said switch actuating means is in a predetermined one of saidtwo positions.

12. In a pressure switch, a switch mechanism movable with inherent snapaction in either direction between two positions, switch actuating meansseparately movable by snap action operably associated with said switchmechanism including a member movably responsive to the force of fluidpressure imposed thereon, means for subjecting said member to fluidpressure, pressure opposing means engaging and imposing a yielding biason said member including a spring having a negative rate and means for13 increasing the sensitivity of said pressure opposing means topressure changes including devices yieldably engaging said member andeffective to decrease the bias imposed on said member by said pressureopposing means when said switch is in a predetermined one of said twopositions.

13. In a pressure switch, a switch mechanism movable with inherent snapaction in either direction between two positions, switch actuating meansseparately movable by snap action operably associated with said switchmechanism including a member movably responsive to the force of fluidpressure imposed thereon, means for subjecting said member to fluidpressure, pressure opposing means engaging and imposing a yielding biason said member including a spring having a negative rate and means forincreasing the sensitivity of said pressure opposing means to pressurechanges including devices yieldably engaging said member effective toincrease the bias imposed on said member by said pressure opposing meanswhen said switch is in a predetermined one of said two positions.

14. In a pressure switch, a switch mechanism movable with inherent snapaction in either direction between two positions, switch actuating meansSeparately movable by snap action operably associated with said switchmechanism including a member movably responsive to the force of fluidpressure imposed thereon, means for subjecting said member to fluidpressure, pressure opposing means engaging and imposing a yielding biason said member, and other means yieldably engaging said member effectiveto decrease the bias imposed on said member by said pressure opposingmeans when said switch is in a predetermined one of said two positionsand to increase the said bias when the switch is in its other position.

15. In a pressure switch, a switch mechanism movable with inherent snapaction in either direction between two positions, switch actuating meansseparately and correspondingly movable by snap action between twopositions operably associated with said switch mechanism and including,a member movably responsive to the force of fluid pressure imposedthereon, means for subjecting a face of said member to fluid pressure,pressure opposing means engaging another portion of said member andimposing a yielding, pressure-opposing bias thereon including a springmember having at least a decreasing rate, and means controlled by saidswitch actuating means additionally yieldably engaging said membereffective to partially oppose the pressure-opposing bias on said memberwhen said switch actuating means is moved to a predetermined one of saidtwo positions by movement of said member.

16. In a pressure switch, a switch mechanism movable with inherent snapaction in either direction between two positions, and switch actuatingmeans separately and correspondingly movable by snap action between twopositions operably associated with said switch mechanism and including,a member movably responsive to the force of fluid pressure imposedthereon, means for subjecting a face of said member to fluid pressure,pressure opposing means engaging another portion of said member andimposing a yielding, pressure-opposing bias thereon including a springmember having at least a decreasing rate, and means controlled by saidswitch actuating means a ditional'ly yieldably engaging said membereffective to increase the pressure-opposing bias on said member whensaid switch actuating means is moved to a predetermined one of said twopositions by movement of said member.

17. In a pressure switch, a switch mechanism movable with inherent snapaction in either direction between two positions, and switch actuatingmeans separately movable by snap action operably associated with saidswitch mechanism and including, a member movably responsive to the forceof fluid pressure imposed thereon, means for subjecting a face of saidmember to fluid pressure, pressure opposing means engaging anotherportion of said member and imposing a yielding, pressure-opposing biasthereon including a spring member having a least a decreasing rate, andmeans controlled by said switch mechanism additionally yieldablyengaging said member effective to partially oppose the pressure-opposingbias on said member when said switch mechanism is in a predetermined oneof said two positions and to increase the said bias when said switchmechanism is in the other of said two positions.

18. A pressure responsive switch including a member yieldably responsiveto imposed fluid pressure, means for subjecting said member to fluidpressure, an electric switch, devices conducting pressure responsivemovements of said member to actuate said switch, means including a discspring engaging and opposing pressure imposed loads on said membernormally effective to maintain said member in a position of repose andoperative both to permit said member to move with snap action from itsposition of repose in response to a predetermined pressure increase andto cause said member to return with snap action to its said position ofrepose upon a drop of at least a predetermined magnitude in the imposedpressure with incident actuation of said switch, and other devicesengaging said member and effective, only during the times when saidmember is in said position of repose, to decrease the extent of pressureopposing bias imposed on said member.

19. A pressure responsive switch including a member, yieldablyresponsive to imposed fluid pressure, means for subjecting said memberto fluid pressure, an electric switch, devices conducting pressureresponsive movements of said member to actuate said switch, meansincluding a disc spring opposing pressure imposed loads on said memberand normally effective to maintain said member in a position of reposeand operative both to permit said member to move with snap action fromits position of repose in response to a predetermined pressure increaseand to cause said member to return with snap action to its said positionof repose upon a drop of at least a predetermined magnitude in theimposed pressure with incident actuation of said switch, and otherdevices effective only during the times when said member is in saidposition of repose, to partially oppose the force exerted on said memberby said disc spring means with resultant reduction in the magnitude ofpressure increase required to cause said member to move from its saidposition of repose.

20. A pressure responsive switch including a member, yieldablyresponsive to imposed fluid pressure, means for subjecting said memberto fluid pressure, an electric switch, devices conducting pressureresponsive movements of said member to actuate said switch, meansincluding a disc spring engaging and opposing pressure imposed loads onsaid member and normally effective to maintain said member in a positionof repose and operative both to permit said member to move with snapaction from its position of repose in response to a predeterminedpressure increase and to cause said member to return with snap action toits said position of repose upon a drop of at least a predeterminedmagnitude in the imposed pressure with incident actuation of saidswitch, and other devices effective only during the times when saidmember is in said position of repose to additively combine a force withthe force exerted by said pressure on said member in opposition to saiddisc spring with resultant decrease in the mag nitude of pressure changerequired to cause said disc spring means to be moved by the pressureimposed load thereon.

21. A pressure responsive switch including a frame, a pressureresponsive member mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port in said frame affordingconnection of said cavity with a source of fluid pressure, an electricswitch including contact making and breaking mechanism, devicesextending between said member and said switch effective to translatepressure responsive movements of said member into movements of thecontact making and breaking mechanism of said switch, means engagingsaid member and including an over-center spring effective to apply abias to said member in opposition to the pressure imposed load andnormally effective to maintain said member in one position and inresponse to a pressure imposed load on said member of -a predeterminedmagnitude, to allow said member to overcome said bias and to move withsnap action to another position and, in response to a pressure decreaseof at least a predetermned magnitude, to allow said means to return saidmember to its said one position, and other means engaging said memberand effective only during the time said member is in said one position,to modify the bias imposed by said first-named means on said member.

22. A pressure responsive switch including a frame, a pressureresponsive member mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port affording connection ofsaid cavity with a source of fluid pressure, an electric switchincluding contact making and breaking mechanism, devices extendingbetween said member and said switch effective to translate pressureresponsive movements of said member into movements of the contact makingand breaking mechanism of said switch, means engaging said member andincluding an over-center spring efiective to apply a bias to said memberin opposition to the pressure imposed load and normally effective tomaintain said member in one position and in response to a pressureimposed load on said member of a predetermined magnitude to allow saidmember to overcome said bias and to move with snap action to anotherposition and, in response to a pressure drop of at least a predeterminedmagnitude, to allow said means to return said member to its said oneposition, and other means effective only during the times said member isin said one position, to partially oppose the force exerted on saidmember by said first-named means with resultant reduction in themagnitude of pressure increase required to cause said member to movefrom its said one position.

23. A pressure responsive switch including a frame, a pressureresponsive member mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port afiording connection ofsaid cavity with a source of fluid pressure, an electric switchincluding contact making and breaking mechanism, devices extendingbetween said member and said switch eifective to translate pressureresponsive movements of said member into movements of the contact makingand breaking mechanism of said switch, means engaging said member andincluding an over-center spring effective to apply a bias to said memberin opposition to the pressure imposed load and normally effective tomaintain said member in one position and in response to a pressureimposed load on said member of a predetermined magnitude to allow saidmember to overcome said bias and to move with snap action to anotherposition and, in response to a pressure drop of at least a predeterminedmagnitude, to allow said means to return said member to its said oneposition, and other means effective, only during the times said memberis in said one position, to additively combine a force with the forceexerted by said first-named means to oppose a pressure imposed load onsaid member with resultant decrease in the magnitude of pressure changerequired to cause said first-named means to move said member inopposition to the pressure imposed load thereon.

24. A pressure responsive switch including a frame, a pressureresponsive diaphragm mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port affording connection ofsaid cavity with a source of fluid pressure, an electric switch, devicesextending between said diaphragm and said switch effective to translatepressure responsive movements of said diaphragm into contact making andbreaking movements of said switch, means engaging said diaphragm andincluding an over-center spring effective to apply a bias to saiddiaphragm yieldingly opposing fluid pressure in said cavity; said meansbeing effective normally to maintain said diaphragm in one position andin response to an increase in the pressure imposed load on saiddiaphragm of a predetermined magnitude to allow said diaphragm toovercome said bias and to move with snap action to another position and,in response to a pressure drop of at least a predetermined magnitude, toreturn said diaphragm to its said one position, and other meanseffective only during the times said diaphragm is in said one position,to modify the bias imposed by said first-named means on said diaphragm.

25. A pressure responsive switch including a frame, a pressureresponsive diaphragm mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port aifording connection ofsaid cavity with a source of fluid pressure, an electric switch, devicesextending between said diaphragm and said switch effective to translatepressure responsive movements of said diaphragm into contact making andbreaking movements of said switch, means engaging said diaphragm andincluding an over-center spring effective to apply a bias to saiddiaphragm yieldingly opposing fluid pressure in said cavity; said meansbeing effective normally to maintain said diaphragm in one position andin response to an increase in the pressure imposed load on saiddiaphragm of a predetermined magnitude to allow said diaphragm toovercome said bias and to move with snap action to another position and,in response to a pressure drop of at least a predetermined magnitude, toreturn said diaphragm to its said one position, and other meanseffective only during the times said diaphragm is in said one position,to partially oppose the force exerted on said diaphragm by saidfirst-named means with resultant reduction in the magnitude of pressureincrease required to cause said diaphragm to move from its said oneposition.

26. A pressure responsive switch including a frame, a pressureresponsive diaphragm mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port affording connection ofsaid cavity with a source of fluid pressure, an electric switch, devicesextending between said diaphragm and said switch effective to translatepressure responsive movements of said diaphragm into contact making andbreaking movements of said switch, means engaging said diaphragm andincluding an over-center spring effective to apply a bias to saiddiaphragm yieldingly opposing fluid pressure in said cavity; said meansbeing effective normally to maintain said diaphragm in one position andin response to an increase in the pressure imposed load on saiddiaphragm of a predetermined magnitude to allow said diaphragm toovercome said bias and to move with snap action to another position and,in response to a pressure drop of at least a predetermined magnitude, toreturn said diaphragm to its said one position, and other meanseffective only during the times said diaphragm is in said one position,to additively combine a force with the force exerted by said first-namedmeans to oppose a pressure imposed load on said diaphragm with resultantdecrease in the magnitude of pressure change required to cause said firnamed means to move said diaphragm in opposition to the pressure imposedload thereon.

27. A pressure responsive switch including a frame, a pressureresponsive means carried by said frame including an aneroid cell havinga flexible, pressure responsive wall, a relatively inflexible wall, andan over-center spring normally urging said flexible wall outwardly awayfrom said inflexible wall in opposition to atmospheric pressure of apredetermined magnitude less than sea level pressure and eifective tocause said flexible wall to move with snap action in response topressure changes of suflicient magnitude both to overcome and to beovercome by the bias of said over-center spring, and devices effective,only during the times when said flexible wall is moved away from 17 saidinflexible wall, to partially oppose the force exerted on said flexiblewall by said over-center spring.

28. A pressure responsive switch as claimed in claim 27 in which saiddevices comprise a solenoid having an armature, a compression springinterposed between said armature and said flexible wall, said solenoidand armature being so disposed that upon energization of the coil ofsaid solenoid said armature through said compression spring will exert aforce against said flexible wall in opposition to the force of saidover-center spring but in suflicient to overcome the force of saidover-center spring until a predetermined amount of atmospheric pressureis exerted on said flexible wall in addition to the force deriving fromthe armature of the energized solenoid.

29. A pressure responsive switch as claimed in claim 28 in which saidswitch includes connections operative to energize the coil of saidsolenoid when said flexible wall is moved outwardly from said inflexiblewall by said over-center spring and to de-energize said solenoid whenthe atmospheric pressure on said flexible wall in addition to the forcederiving from the energized solenoid overcomes the bias of saidover-center spring.

30. A pressure responsive switch including a member yieldably responsiveto imposed fluid pressures, means for subjecting said member to fluidpressure, an electric switch, and devices effective to cause said memberto respond to imposed fluid pressure with snap action includingover-center spring means operative to bias said member to yieldablyoppose pressure imposed loads thereon, said devices including a solenoidhaving a coil electrically connected to said switch, an armature, andyielding means forming an operative interengagement between saidarmature and said pressure responsive member; said coil being energizedonly when said member is in its said position of repose and saidsolenoid being then effective to activate said armature with resultantmodification of the magnitude of pressure imposed load upon said memberrequired to cause said member to move with snap action in opposition tothe bias of said over-center spring means.

31. A pressure responsive switch including a member yieldably responsiveto imposed fluid pressures, means for subjecting said member to fluidpressure, an electric switch, and devices effective to cause said memberto respond to imposed fluid pressure with snap action includingover-center spring means operative to bias said member to yieldablyoppose pressure imposed loads thereon, and devices including a solenoidhaving a coil electrically connected to said switch, an armature, andyielding means forming an operative interengagement between saidarmature and said pressure responsive member; said coil being energizedonly when said member is in its said position of repose and saidsolenoid being then effective to partially oppose the force exerted onsaid member by said over-center spring means with resultant reduction inthe magnitude of pressure increase required to cause said member to movefrom its said position of repose.

32. A pressure responsive switch including a member yieldably responsiveto imposed fluid pressure, means for subjecting said member to fluidpressure, an electric switch, devices conducting pressure responsivemovements of said member to actuate said switch, negative rate springmeans opposing pressure imposed loads on said member normally effectiveto maintain said member in a position or" repose and operative both topermit said member to move with snap action from its position of reposein response to a predetermined pressure increase and to cause saidmember to return with snap action to its said position of repose upon adrop in the imposed pressure of at least a predetermined magnitude withincident actuation of said switch, and other devices eflective to modifythe magnitude of pressure imposed loads on said member required to causesaid member to move from its said position of repose; said other devicesincluding a cylinder, a piston mounted in said cylinder, a

train of mechanism establishing a yielding interengagement between saidpressure responsive member and said piston, and valve means forintroducing fluid pressure into said cylinder only during the time saidpressure responsive member is in its said position of repose and forrelieving said cylinder from pressure at all other times.

33. A pressure responsive switch including a member yieldably responsiveto imposed fluid pressure, means for subjecting said member to fluidpressure, an electric switch, devices conducting pressure responsivemovements of said member to actuate said switch, negative rate springmeans opposing pressure imposed loads on said member normally effectiveto maintain said member in a position of repose and operative both topermit said diaphragm to move with snap action from its position ofrepose in response to a predetermined pressure increase and to causesaid diaphragm to return with snap action to its said position of reposeupon a drop in the imposed pressure of at least a predeterminedmagnitude with incident actuation of said switch, and other deviceseffective to partially oppose the force exerted on said diaphragm bysaid negative rate spring means with resultant reduction of themagnitude of pressure increase required to cause said member to movefrom its said position of repose; said other devices including acylinder, a piston mounted in said cylinder, a train of mechanismestablishing a yielding interengagement between said diaphragm and saidpiston, and means for introducing fluid pressure into said cylinder onlyduring the time said diaphragm is in its said position of repose and forrelieving said cylinder from pressure at all other times.

34. A pressure responsive switch including a member yieldably responsiveto imposed fluid pressure, means for subjecting said member to fluidpressure, an electric switch, devices conducting pressure responsivemovements of said member to actuate said switch, negative rate springmeans opposing pressure imposed loads on said member normally effectiveto maintain said member in a position of repose and operative both topermit said member to move with snap action from its position of reposein response to a predetermined pressure increase and to cause saidmember to return with snap action to its said position of repose upon adrop of the imposed pressure of at least a predetermined magnitude withincident actuation of said switch, and other devices effective toadditively combine a force with the force exerted by said negative ratespring means to opposea pressure imposed load on said member withresultant decrease in the magnitude of pressure change required to causesaid negative rate spring means to move said member in opposition to thepressure imposed load thereon; said other devices including a cylinder,a piston mounted in said cylinder, a train of mechanism establishing ayielding interengagement between said pressure responsive member andsaid piston, and valve means for introducing fluid pressure into saidcylinder only during the time said pressure responsive member is in itssaid position of repose and for relieving said cylinder from pressure atall other times.

35. A pressure responsive switch including a frame, a pressureresponsive diaphragm mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port aflording connection ofsaid cavity with a source of fluid pressure, an electric switch, devicesextending between said diaphragm and said switch effective to translatepressure responsive movements of said diaphragm into contact making andbreaking movements of said switch, means including a negative ratespring effective to apply a yielding, pressure opposing bias on saiddiaphragm and normally effective to maintain said diaphragm in oneposition and in response to an increase in the pressure imposed load onsaid diaphragm of a predetermined magnitude, to allow said diaphragm toovercome said bias and move with snap action to another position and inresponse to a pressure drop of at least a predetermined magnitude toallow said over-center spring means to return said diaphragm to its saidone position, and other means effective only during the times saiddiaphragm is in said one position to modify the bias imposed by saidover-center spring means on said member; said other means comprising asolenoid, an armature associated with said solenoid, means establishinga yielding interengagement between said armature and said diaphragm andelectrical connections extending between the coil of said solenoid andsaid switch effective to energize said coil only during the time saiddiaphragm is in its said one position, the energization of said coilbeing effective to cause said armature acting through said interengagingmeans to impose a load on said diaphragm in opposition to the biasimposed thereon by said negative rate spring means.

36. A pressure responsive switch including a frame, a pressureresponsive diaphragm mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port affording connection ofsaid cavity with a source of fluid pressure, an electric switch, devicesextending between said diaphragm and said switch effective to translatepressure responsive movements of said diaphragm into contact making andbreaking movements of said switch, means engaging said diaphragm andincluding a negative rate spring effective to apply a yielding, pressureopposing bias on said diaphragm and normally effective to maintain saiddiaphragm in one position and in response to an increase in the pressureimposed load on said diaphragm of a predetermined magnitude, to allowsaid diaphragm to overcome said bias and move with snap action toanother position and in response to a pressure drop of at least apredetermined magnitude to allow said means to return said diaphragm toits said one position, and other means effective only during the timessaid diaphragm is in said one position to modify the bias imposed bysaid first-named means on said member; said other means comprising asolenoid having a coil and an armature, electrical connections extendingbetween said switch and said coil, devices establishing a yieldinginterengagement between said diaphragm and said armature, said armatureand said coil of said solenoid being so constructed and arranged thatupon energization of said coil said armature acting through saidinterengaging devices will additively combine with the force exerted bysaid firstnamed means on said diaphragm to oppose a pressure imposedload on said diaphragm with resultant decrease in the magnitude ofpressure change required to cause said first-named means to move saiddiaphragm in opposition to the pressure imposed load thereon.

37. A pressure responsive switch including a frame, a pressureresponsive diaphragm mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port in said frame affordingconnection of said cavity with a source of fluid pressure, an electricswitch, devices extending between said diaphragm and said switcheffective to translate pressure responsive movements of said diaphragminto contact making and breaking movements of said switch, meansengaging said diaphragm and including an over-center spring effective toapply a yielding, pressure opposing bias on said diaphragm and normallyeffective to maintain said diaphragm in one position and in response toan increase of predetermined magnitude in the pressure imposed load onsaid diaphragm, to allow said diaphragm to overcome said bias and tomove with snap action to another position and, in response to a pressuredrop of at least a predetermined magnitude, to allow said means toreturn said diaphragm to its said one position, and other meanseffective to modify the magnitude of pressure imposed load on saiddiaphragm required to cause said diaphragm to move from its said oneposition; said other means including a cylinder, a piston mounted insaid cylinder, a train of mechanism establishing a yieldinginterengagement between said diaphragm and said piston, and means forintroducing fluid pressure into said cylinder only during the times saiddiaphragm is in said one position and for relieving said cylinder frompressure at all other times.

38. A pressure responsive switch including a frame, a pressureresponsive diaphragm mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port in said frame affordingconnection of said cavity with a source of fluid pressure, an electricswitch, devices extending between said diaphragm and said switcheffective to translate pressure responsive movements of said diaphragminto contact making and breaking movements of said switch, meansengaging said diaphragm and including an over-center spring effective toapply a yielding, pressure opposing bias on said diaphragm and normallyeffective to maintain said diaphragm in one position and in response toan increase of predetermined magnitude of the pressure imposed load onsaid diaphragm, to allow said diaphragm to overcome said bias and tomove with snap action to another position and, in response to a pressuredrop of at least a predetermined magnitude, to allow said means toreturn said diaphragm to its said one position, and other meanseffective to partially oppose the force exerted on said diaphragm bysaid first-named means with resultant reduction in the magnitude ofpressure increase required to cause said diaphragm to move from said oneposition; said other means including a cylinder, a piston mounted insaid cylinder, a train of mechanism establishing a yieldinginterengagement between said diaphragm and said piston, and valve meansfor introducing fluid pressure into said cylinder only during the timessaid diaphragm is in its said one position and for relieving saidcylinder from pressure at all other times.

39. A pressure responsive switch including a frame, a pressureresponsive diaphragm mounted on said frame and cooperating therewith todefine a pressure fluid receiving cavity, a port in said frame affordingconnection of said cavity with a source of fluid pressure, an electricswitch, devices extending between said diaphragm and said switcheffective to translate pressure responsive movements of said diaphragminto contact making and breaking movements of said switch, meansengaging said diaphragm and including an over-center spring effective toapply a yielding, pressure opposing bias on said diaphragm and normallyeffective to maintain said diaphragm in one position and in response toan increase of predetermined magnitude of the pressure imposed load onsaid diaphragm, to allow said diaphragm to overcome said bias and tomove with snap action to another position and, in response to a pressuredrop of at least a predetermined magnitude, to allow said means toreturn said diaphragm to its said one position and other means effectiveto additively combine a force with the force exerted by said first-namedmeans to oppose pressure imposed load on said diaphragm with resultantdecrease in the magnitude of pressure change required to cause saidfirst-named means to move said diaphragm in opposition to the pressureimposed load thereon, said other means including a cylinder, a pistonmounted in said cylinder, a train of mechanism establishing a yieldinginterengagement between said diaphragm and said piston, and valve meansfor introducing fluid pressure into said cylinder only during the timessaid diaphragm is in its said one position and for relieving saidcylinder from pressure at all other times.

References Cited in the file of this patent

